Generally, three-dimensional (3D) medical imaging systems refer to systems for providing medical data as visual information useful for diagnosis using various techniques. In this case, the medical data refers to data that is created by reconstructing information about a bodily organ in a superimposed cross sectional form, obtained through Computerized Tomography (CT) or Magnetic Resonance (MR), into a 3D form.
Recently, with the rapid advance of the technology of medical imaging equipment such as a CT scanner or an MR scanner, a precise image can be acquired within a short period of time. Actually, in hospitals, hundreds or thousands of images are being generated for a single medical examination. Meanwhile, although such a large amount of image information provides useful diagnosis information, it takes an excessively long time and many efforts to read images one by one, as in a conventional method of reading two-dimensional (2D) images.
A system that was developed to overcome the above problem is a 3D medical imaging system. This system renders 3D medical image data as visual information useful for diagnosis using a Direct Volume Rendering (DVR) technique, a Maximum Intensity Projection (MIP) rendering technique, and a Multi Planar Reformatting (MPR) technique.
A common 3D medial image rendering technique is performed based on a viewpoint, the direction of a line of sight, a plane containing an output scene, and a model composed of a target object, and may be described with reference to FIG. 1.
FIG. 1 is a diagram illustrating a general 3D rendering method. Referring to FIG. 1, in the case of the general 3D rendering method, a rectilinear line that connects a pixel of an output scene 2 and a viewpoint 1 is referred to as a ray 3. A final scene is generated by applying various techniques to densities obtained by sampling individual points while the ray 3 is passing through volume data 5.
In this case, the MIP rendering technique, which is one of the 3D rendering methods, is a method of finding a maximum density while moving along a ray. Meanwhile, since the MIP technique renders a scene while taking into account only the maximum value of density, this scene is characterized in that depth information is lost unlike in a DVR scene, and thus a disadvantage arises in that a user estimates depth while frequently changing an observation direction.
In order to overcome this problem, research into a technology for generating MIP scenes at rapid speed to deal with frequent changes in an observation direction has been conducted in various manners. As an example of this technology, there is a so-called leaping technique that determines an unnecessary area of medical data determined not to be incorporated into a final output scene and then skips the calculation thereof.
However, although the leaping technique has the advantage of accelerating the generation of a final scene without influencing image quality, it has a disadvantage in which the time required to detect the unnecessary area and the amount of additional memory required to store information about the unnecessary area must be taken into account.
For example, a method for sorting overall data constituting a medical scene in descending order of density values and then starting rendering from the highest value has problems in that a long sorting time is required and the amount of additional memory is large.
Meanwhile, Korean Patent No. 10-1075014 entitled “Method of Accelerating MIP Rendering Using Parallel Ray Casting and Space Leaping” relates to a method of accelerating MIP rendering, which generates a plurality of medical scenes, photographed by 3D medical imaging equipment, as visual information useful for diagnosis. In particular, this patent proposes a method of accelerating MIP rendering using ray casting, which can reduce preprocessing time by means of a method that performs ray casting and block processing in parallel and moves through blocks while comparing a ray value with a per-block maximum value, and which can rapidly acquire MIP scenes using only general-purpose hardware.
This preceding technology is directed to a technology that combines a plurality of voxels into blocks, acquires brightness and a maximum value for each of the blocks, compares the acquired value with a maximum value for a ray under current calculation, and then performs a block-based leaping, thereby reducing time. This technology aims to reduce computational load in a single ray by performing a block-based leaping when acquiring a maximum value in the single ray, but does not take into account the order of the calculations of a plurality of rays.